Twitter Bower has been around since last week and it's getting a mixed reception from the community of developers that have stumbled upon it so far.
It's too early perhaps to get an opinion on it, the fact that Twitter hasn't made an announcement signals that the tool is not ready yet. That said, Bowler may have been in use internally for a while and Twitter is now open-sourcing it.
Twitter has a history of open-sourcing internal tools, Twitter's Bootstrap
has been very popular with developers and has recently gotten a major update. Twitter is hardly alone in this, most big tech companies open source internal tools or technologies and rely extensively on other open-source projects.
is available for download here